Automatic frequency controller



Jan. 6, 1931 J. WOLF 1,788,073

" AUTOMATIC FREQUENCY CONTROLLER Filed May 26; 1928 b5 -5 "T E g INVENTOR Lester J.Woh

- ATTORNEY msrrradiated from said station. This -modula-' in a receiving set ata short Patented Jan. 6, 1931 A UNITED s'r 'rEs PATENT; OFFICE.

ms'ran i. WOLF, orsonrn nmvn, mnmna, assrenon "r wasrmsnousn- ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA in'u'mmmrc raaaurmer comma Y Application m m 26, 1928. Serla1 110. 280,730.

This invention relates to relaying systems for radio communication and particularly to systems in which two radio transmitting stations at a distance apart are to be maintained 5 at exactly the same wave length;

- W This invention is an improvement upon the invention of Patent No. 1,781,263, issued November 11, 1930, to the Westinghouse Electric and Manufacturing Company upon an,appli-, o cation filed by me.

In the system describedin deta ilrin application, a tunmg fork at thehome station impresses a modulation upon the energy tionlproduces,

, distance from the distant station, a current offa frequency corresponding to that of the fork at the home station. The energy from the receiving wt I 'oscillatiofi'system at the distant station which comprises a tuning fork and regenerative circuits associated with i As explained in said co-pending applicanearly as possible to the same'natural frequency, and the regenerative circuits at the istant station are caused to further so adjust 40' the frequencythat the natural periods of the twooscillatin systems are very nearly equal, it is not possi 1e to produce absolute equality of these natural frequencies. Consequently,

1 other cause, the fork at the home station is impressed upon a local the influence of its regenera when, because of fading or' oeasesto control the fork at the distant sta tion, the two forks will become outof phase.- If, after such an event, the interruption ends and the fork at the home station can again produce an influence at the distant station,

the incorrect phase relation may cause this influence to tend to stop the fork at the distant station, which would result in an interruption of broadcasting from-the distant station.

' It is alnobj eet of thisinventimoid such interruptions.

It is a further object of'this invention to provlde automatic means whereby, if the phase of the impulses originating from thefork at the home station and arriving at the distant station is such that the impulses are opposite in sense to the currents. in the oscillating system at the distant station, these impulses will be prevented from bringing the fork'at the distant station torest or from materially diminishing its amplitude.

' It is a further object of this invention to provide a control device whereby, when the currents generated by the fork and the cur-' rents produced by the receiving set at the distant station are subtract-ively and not additivelyrelated, thecurrents produced by the receiving set will be shunted away from the oscillating-system.

Other objects of the invention and details of the construction will be understood from the following description and the accom panying drawing in which the single figure:

is a diagram of employed.

In the drawing, the sending set 1 is ,at the home'station. It is intended tosend out either a frequency produced by. a tuning fork at the sending station or 'a' high fre-' quency modulated y the frequency of the fork. The antenna 2 at the receiving stathe circuits and apparatus tion'is connected to a receiving set 3 which is tuned to the signals sent but by sending" set paratus at the distant station. Adjustment of the receiving set must, therefore, be controlled over a line l, and the key 5 is for such control. Between line 4 and the con trally located apparatus at the distant station, a filter 6 is provided. This filter is of the type which Will deliver only currents of tration, this connection to the relay is shown as associated with, the input circuit of the frequency multiplier but it may equally well be included in the connection to the grid of any of the tubes in said multiplier.

The contacts of the relay 38 control a shunt 39 which preferably includes a resistor 40, the shunt extending across the grid-filament connection of any one of the device including tubes 16 and 17 arranged in cascade. r

a frequency determined by the fork at. the tubes between the transformer 30 and the sending station. '---magnet-23,-Bir ferab ly, however, one of the At the distant station the fork 10 is tuned, tubes in the amplifier, between the fransas closely as can conveniently be done, to former 30 and the transformer 33, is chosen. the frequency of the fork at the, station 1. In the operation of the device, the receiv- Details of the provisions for maintaining ing set 3 delivers to the line 4 currents of. a this fork at constant temperature and thus frequency determined by. the fork in the insuring its constant frequency are described sending set 1. Preferably, this frequency is in the above-mentioned co-pending applicavery close to'the frequency of the fork 10. tion. Any suitable means for adjusting the re- A regenerative system of circuits is proceiving set 3 may be controlled over the line vided whereby the fork may be maintained 4 by means of the key 5, and the receiving in vibration even when no energy is received set may thus be adjusted to best conditions from the receiving set 3. These regenerafor delivering impulses of the fork fi'etive circuits include a coil 11 mounted upon quency to the filter 6. Impulses of a freone tine of the fork. Electromotive forces, quency very different from this will fail to developed in this coil by the vibration of the traverse the filter 6. The transformer 30, fork, establish currents through the resistor therefore, will deliver to the tube 31 im- 12 and so impress a potential upon the grid ul f o l th f k frequenc of a tube 13. The potentials amplified by Such impulses, amplified by t e cascade this tube are delivered, through a condenser amplifier including tubes 31 to 17 inclusive, 14 and a transformer 15, to an amplifying cause the magnet 23 to impress a periodic force upon the fork 10. Since this periodic The output of this amplifier is delivered, as the natural ffequency of the fork, the fork through a filter, including condensers 18 will have forced vibrations of the frequency and 19 in series and an inductor 20 in parof the impulses received over the line 4:.

allel, to a magnet 23-whi'ch drives the fork Only a small part of the energy needed to 10. The inductor 20 is made adjustable in maintain the fork in vibration comes over order to assist in controlling the frequency thedin 4, The vibration of the fork, by of the fork 10. A still closer control over d Y i ti f i th i da d que y is rded y t e u e 24 ing 11, deliversen ergy, rough the tube 1.3 which is controlled by the grid-biasing deand condenser 14, to th input, circuit vice 25., tube 16. The tubes 16 and 17, with their force is of very nearly the samehfrequency The energy delivered to the transformer associated circuits, and the tube 13, with 15 through the tube 13 is pp n y its associated'circuits, constitute a regeneraenergy from the tra s or r 30 w (3011'- tive system of circuits which cooperates with neots the filter (H0 a c cade a ph y g sy the fork 10 to maintain it in vibration. tem including tubes 31 d 3 and The regenerative action of this system is former 33. sufficient to maintain the fork in vibration, The potential across reslstor 12 1S de indefinitely or, at least for a period of several cred t0 the Input clrcillt Of a q e y m seconds after impulses cease to arrive over tiplier 35. The frequen y multipli r may the line 4. The fork 10 and the tubes 13 to be of any preferred form but, for my pur- 17, with their associated circuits, may thus poses, I have found the o m t at in be regarded as a local source of oscillation Fig. 3 of the above-mentioned co-pending of nearly the same frequency as the impulses application to be convenient. .The multiarriving over the line 4; plier may include a number of vacuumtubes. The electromotive force delivered by the The input circuit of such a frequency mulcoil 11 not only acts upon the tube 13 but also tiplier is connected to the grid and filaacts upon the frequncy multiplier 35. In ment of the first of said vacuum tubes. order that any harmonics of the fundamen- In the connection to' the grid of any of tal frequency which may be useful in assistsaid tubes, a condenser 36 is inserted, and ing in the production of higher frequencies leads 37 from the two sides of the condenser in the frequency multiplier shall not be lost, extend to the winding38 of a relay biased as condenser 36 bridges an openin in the' to closed position. For convenience of illusconnection between the coilll and the input amplitude, the ,current delivered to the winding 38 is sufficient to maintainnthe contacts of the relay open against the bias thereof. The shunt 39 is, therefore, open and without effect upon the tube 31.

The circuit through the winding 38 extends from the upper end of the resistor 12 through the leads 37 and said winding to the grid of the first tube of the frequency multi her and from the filament of said tube to t e lower end of the resistor 12. The rectifying action of the filament and grid in said' first tube gives a unidirectional character to the force exertedby the winding 38 upon the contacts of the relay.

The bias of the relay to closed position may, therefore, properly be a magnetic bias such as polarized relays ordinarily possess. The

spring shown upon the drawing may be con-.

, sidered as representing either a mechanical bias ora magnetic bias. I

The magnitude of this bias is so chosen that, normally, the current in winding 38 is just suflicient to hold the relaycontacts open. The nornfal condition is that in which the output from the -local source comprising thev 'fork and its associated regenerative system of circuits is neither increased'nor diminished by energy from the transformer 33.

When fading or failure of the fork at the sendingstation 1, or any other cause, produces an interruption in the periodic currents over the line 4, no energy is delivered over the transformer 33 to the input of the regenerative sfystem. The energy delivered to the input 0 the frequency multiplier, that regenerative system will become somewhat smaller as the amplitude of the fork 10 diminishes because of the failure ofenergy .from the transformer-33. This diminution in the output of the regenerative system will vbe'slowybecai1se the regenerative system is nearly suflicient to maintain the fork in vibration at normal amplitude.

Even though the amplitude of the output f changesbut slightly, the frequency of the.

' out ut will change. The change in frequency wi .not be large because the natural period of the local oscillating. device is nearly the same as the period of the impulses'normally arriving over the line 4. The change in fre-. que'ncy will however, be. enough-to produce" .a beat note in receiving sets listening both to the sending set 1 and the sendin set energ'izedv through the frequency mu tiplier 35. This beat note is objectionable but not as objectionable as an interruptiog grolaldcastfl. P Q. 1 3

ing" from'the transmitter su the multiplier 35 would be.

The natural frequency of the local oscillating device-is. not-the same as that of the currents over the line 4. Consequently, when these currents cease, aslowly varying phase 4 difierence'will arise between the ork at the sending station 1 and the fork 10. When the If, therefore, the hase difference be sufficient, the energy'de ivered to the transformer 15 may actually be less when the interruption is over than it was during said interruption. This will result in a diminution in the amplitude of the vibration of the fork -10.

If the energy delivered over the line 4 is opposite in phase to that delivered over the condenser 14, the diminution in amplitude of the fork may be very rapid. Even of the diminution isnot rapid, it will unless prevented, continue until the fork has been brought to rest or nearly to rest. Then, until the fork has had time enough to again buildv u oscillations in phase with those at the stationl, little or no energy will be delivered to the frequency multiplier 35 and little or no energy will be broadcasted cally, but vectorially in'the transformer 15.

through the transmitter to which this mul- T tiplie'r is connected The diminution in current in the output 12 of the regenerative system, which accome pames the diminution in amplitude of the vibrations of the fork, causes a diminution of current in the winding 38, with-the result tube 31. The energy which the amplifier, ir'u.

eluding the tube 31, would deliver to the transformer"15' is now largely prevented from reaching the amplifier. The resistor 401s of such magnitude that some energy from the transformer 30 is delivered to the amplifier and, therefore, to the regenerative system, but this energy is insufiicient 'to produce any ob ectionable diminution in the amplitudeof the fork.

While the shunt 39 is closed, the regenerative systemincluding the fork 10, continues,

to oscillate at its natural frequency, and therefore, continues to change its phase relation to the-ener After the lapse o sufiicient. time, not more than a half cycle of the beat note between the twonearly equal frequencies, the phase of the impulses from the transformer 30 and. coil 11 will'be such that theyproduce an additive efiect inthe transformer 15.

.. Because OfLthB resistor 40'the energy arrive ing at the transformer 33, when the shunt 39 is closed, is suflicientto'produce some 'in- 12o 1n the transformer 30. I

crease in the energy of the regenerative system when the phase relation is such that the two currents add. When this occurs, an increase in the amplitude of the fork results. There will, therefore, be an increase in the output of the regenerative system. This includes an increase in current in the winding 38. Therefore the relay 38 will overcome its bias and the shunt 39 will be opened.

As soon as the shunt is opened, full benefit of the energy from the transformer will be received, and the amplitude of the fork 10 will quickly build up to full value, the frequency of the fork 10 being now controlled by the currents in the line 4 and, therefore, producing no heat note in the receiving sets of listeners. I

It will thus be seen that, although the relay 38 results in a prolongation of the time during" which the listeners hear a beat note, it

will prevent the actual interruption of boardcasting service.

The operation has been described 'with the bias on the relay 38 insufiicient to keep the relay contacts closed when normal current is present in the winding 38. An operative system may equally well be made with the relay so adjusted that the current from the fork is normally insufiicient to hold the relay open. That is, when no current is being received over the line .4, the current in the' Winding 38 is just insufficient to cause the contactsto open;

- For this adjustment of the bias, the resistor 40 must have somewhat less resistance than for the adjustment used in the operation first described.

'An interruption of the current in line 4-, such as results from fading, will cause no change in the position of the relay contacts because they are already closed. When,

after an interruption, current reappears in the line the presence of the resistor 40 in the shunt Wlll cause this current to produce some effect on' the magnitude of the current in Winding 38. 'If this effect is additive, the shunt will open and the currents in ,line 4 will then have full effect in restoring the frequency of the fork to its correct value. on the other hand, these currents are of incorrect phase, the relay contacts remain closed, and the energy delivered through the transformer 33 will be insufiicient to produce any marked effect upon the frequency of the fork. 7

Many variations in the details of the'system will be apparent to those skilled in the art and many other applications of the invention besides that specificallv described and illustrated will also be apparent. I do not intend, therefore, to be limited except as required by the-prior art and as indicated in the accompanying claims.

- I claim as my lnventlon:

1. Inga synchronizing system, a local oscillation device having a natural frequency,

a distant source of oscillations,'means con-.

trolled by said distant source for impressing on said local device periodic energy of nearly the same period as said natural frequency to constrain said localdevice to oscillate at a frequency determined by said distant source and means for preventing said constraining action from causing an interruption of the oscillation of-said local device.

3. Means for controlling the frequency of an oscillating system from a distance, comprising regenerative connections forming part of said system, a frequency-selective receiving device adjusted to be responsive to arriving signals of a frequency approximately that of the natural period of the oscillation system, means for delivering inipulses from said receiving set to said regenerat'ive connections and automatic means for diminishing the effect of Sn cl impulses upon said oscillating system whenever the sense of the impulses is opposed to that of the oscillations.

4. In a synchronizing system, a device having a natural period of mechanical vibration, a regenerative system associated therewith to maintain said device in vibra'-, tion, means controlled from a distance for impressing on said regenerath'e system oscillatory energy of a period nearly equal to said natural period, whereby forced oscillations are maintained in said regenerative sys tem ip synchronism with said oscillatory energy, means for diverting :aid oscillatory energy and means controlled by the resultant current in said regenerative-system for controlling said diverting means.

5. In a synchronizing system, a device having a natural period of mechanical vibration, circuits forming with said device a regenerative system constituting a localoscillation device, a distant source of oscillations, a receiving set tunedto respond to energy from said distant source, connections between said receiving set and said regenerative system, whereby oscillatory energy of a period fixed by said distant source will be impressed on said local oscillation device thefrequency of said distant source being such that said oscillatory energy will have a period near said natural period whereby said local oscillation device will be constrained to oscillate at a frequency fixed by said distant source, a'shunt across said conoutput connections from said regenerative nections, a relay controlling said shunt and o LESTER J. WOLF. 

